The invention relates to a drier for objects, particularly for vehicle bodies, comprising
a) a housing, in which is formed a drying chamber which accommodates the objects;
b) a connection for intake air;
c) a connection for exhaust air;
d) at least one catalytic radiator which, in turn, comprises:                                    da) at least one connection for combustion gas;            db) a catalytically active layer to which the combustion gas is supplied;            dc) at least one connection for combustion air, connected to the catalytically active layer via an air duct;                        
and to a method for operating a drier for objects, particularly vehicle bodies, in which
a) the objects to be dried are brought into a drying chamber in the housing of the drier;
b) in the drying chamber, the objects to be dried are exposed to an infrared radiation generated by a catalytic radiator to whose catalytically active layer combustion gas and combustion air are supplied;
c) intake air is continuously supplied to, and exhaust air continuously extracted from, the drying chamber.
Driers which operate with catalytic radiators as a heat source are becoming increasingly popular. There is a good reason for this: firstly, the primary energy used, namely, the combustion gas (natural gas, propane, butane or liquid gas) is very inexpensive compared with electrical energy. Secondly, with such catalytic radiators, it is possible to generate an infrared radiation in that long-wave range which is particularly effective for drying or firing coatings, particularly paint coatings. Energy savings are also achieved in that, substantially, only the coating to be dried is heated, but not other objects.
In addition, the long-wave radiation of a catalytic radiator has the characteristic of gently heating and drying the object with an energy density which is moderate compared with short-wave or medium-wave radiation.
It has already been previously recognized that organic impurities, contained in the combustion air supplied to the catalytic radiator, are catalytically oxidized in the catalytically active layer of catalytic radiators. Hitherto, however, this fact has only been considered as a fortunate side effect of the use of catalytic radiators, and has not been purposefully used. In the case of the known driers of the initially stated type, this was also not possible, because these catalytic radiators used, which needed an air cooling, or the air duct was not defined inside the drier. In those cases, there was thus brought into the drying chamber intake air which was not constrained to flow over the catalytically active layer. Impurities contained in this intake air thus remained unoxidized, with the result that the exhaust air extracted from the drier had to be supplied to a separate exhaust-air purification appliance, for example, a thermal, regenerative or even a catalytic post-combustion appliance. These appliances then frequently served as a general disposal system for all exhaust-air volume flows loaded with organic substances, particularly solvents, that occurred in the installation as a whole, i.e., not only in the drier. In the case of painting installations, these typically come from, in particular, the spraying booth, the flashing-off zone, the drier, the paint mixing room or from other sources.
The additional exhaust-gas purification appliances that are thus necessary in the case of the known driers of the initially stated type obviously give rise to relatively high costs.
An object of the present invention is to design a drier of the initially stated type in such a way that it is possible to dispense with a separate exhaust-gas purification appliance or the quantities of exhaust air produced are at least reduced, so that the separate exhaust-gas purification appliance can be kept smaller, and therefore less expensive.
This object is achieved, according to the invention, in that
e) the connection of the drier for intake air is connected exclusively to the connection of the catalytic radiator for combustion air, in such a way that, apart from unavoidable leakages of the housing, all the intake air is routed as combustion air via the catalytic radiator;
f) the catalytic radiator is of heat resistant design, such that it does not require air cooling.
The concept according to the invention is as follows: if catalytic radiators are used which do not require air cooling, all the intake air brought into the drying chamber of the drier can be directed in a constrained manner via the connection of the catalytic radiator for combustion air, so that all intake air passing into the drying chamber has flowed at least once past the catalytically active layer or through the catalytically active layer. In this way, it becomes possible for the catalytic oxidative transformation of the organic impurities in the intake air to be performed as a controlled reaction, quantitative predictions of the reaction conversion also being possible.
In favourable cases, a single passage of the intake air through the catalytically active layer of a catalytic radiator is sufficient to effect adequate purification.
The intake air supplied to the drier in this case can originate partly from the drier itself, but also from other parts of an installation, so that the drier, as a “general disposal facility” for the entire installation, can fully or partially replace the separate exhaust-air purification appliances previously provided for this purpose.
The catalytic radiator can have a connection via which exclusively intake air is supplied to it. This intake air is directed within the catalytic radiator to a location from which it can flow against a surface of the catalytically active layer in a defined manner. As a result, conditions are created in which there occurs a controlled transformation of the organic impurity contained in the intake air.
An even greater efficiency is achieved in the case of that embodiment of the invention in which the catalytic radiator has a connection which is connected to a premixer in which combustion gas and intake air are mixed together. This mixing of combustion gas and intake air containing pollutants, which occurs even before they enter the catalytic radiator, promotes the catalytically activated oxidation of the organic impurities, so that a greater degree of transformation is achieved.
A blower, by means of which the air in the drying chamber can be circulated, can be provided for the purpose of convective heating of the objects to be dried.
In those cases in which adequate purification is not yet achieved with a single passage of the intake air through the catalytically active layer of a catalytic radiator, it is possible to use an embodiment of the invention in which the drier is of a multi-stage design, each stage being designed in the manner described in one of claims 1 to 4, and the exhaust-air connection of the respectively upstream stage being connected to the intake-air connection of the respectively downstream stage. In this way, in passing through the drier, the intake air supplied to the drier passes several times through a catalytically active layer of a catalytic radiator, with the result that the transformation of the organic impurities is effected in a more complete manner. In principle, any number of such stages can be provided, until the required degree of purification is achieved.
A further object of the present invention is to disclose a method for operating a drier of the initially stated type, in which the catalytic radiators contained in the drier can be used in a purposeful and controllable manner for purifying the intake air supplied to the drier.
This object is achieved, according to the invention, in that
d) all the intake air supplied to the drying chamber, apart from unavoidable leakages of the housing of the drier, is routed as combustion air via the catalytically active layer of the catalytic radiator;
e) a catalytic radiator is used which is of heat resistant design, such that it does not require cooling.
The advantages of this method according to the invention correspond analogously to the above-mentioned advantages of the drier according to the invention.
Advantageous developments of the method according to the invention are disclosed in claims 6 to 10. The advantages that can be achieved with them also correspond to the above-mentioned advantages of particular embodiments of the drier.